A total of 20 amounts are entered on a spreadsheet that has 5 rows and 4 columns; each of the 20 positions in the spreadsheet contains one amount. The average (arithmetic mean) of the amounts in row i is Ri (1 ≤ i <≤5). The average of the amounts in column j is Cj (1 ≤ j ≤ 4). What is the average of all 20 amounts on the spreadsheet?

(1) R1 + R2 + R3 + R4 + R5 = 550

(2) C1 + C2 + C3 + C4 = 440


Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

EACH statement ALONE is sufficient.

Statements (1) and (2) TOGETHER are NOT sufficient.

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题目分析：

求20个值的平均值，即求得20个值的和即可。

（1）  每一行的4个数的和为4Ri，所以5行共20个数的和为4~$(R_1+R_2+R_3+R_4+R_5)=4*550=2200$~，20个数的平均数为2200/20=110，题目得解。

（2）  每一列5个数的和为5Cj，所以4列共20个数的和为~$5(C_1+C_2+C_3+C_4)=5*440=2200$~，20个数的平均数为2200/20=110，题目得解。

因此，本题答案为（D），任何一个条件说明均能解题。

 

 

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